This application claims the benefit of German Application No. 201 10 553.3 filed Jun. 26, 2001.
The invention relates to a steam motor with a piston engine. The piston engine is included in a closed steam circuit. This steam circuit includes a steam generator, a steam injector for injecting steam into the piston engine, a condenser for condensing the steam emerging from the piston engine to condensed water, and a water feeding pump for feeding the condensed water to the steam generator. The steam generator is heated by hot combustion gas from a combustion unit. The combustion unit burns fuel. The fuel is mixed with fresh air supplied by an air feeding device through a fresh air passage. The fresh air passage usually contains a first heat exchanger for pre-heating the fresh air by heat from the expanded steam emerging from the piston engine, and a second heat exchanger for preheating the fresh air by heat from hot waste gas emerging from the steam generator.
Such a steam motor of this type is described in detail in papers xe2x80x9cZero Emission Enginexe2x80x94Der Dampfmotor mit isothermer Expansionxe2x80x9d, MTZ Motortechnische Zeitschrift 61 (2000), 5 and xe2x80x9cDer Dampfmotorxe2x80x94Entwicklungsstand und Marktchancenxe2x80x9d, MTZ Motortechnische Zeitschrift 62 (2001), 5. The steam motor has a three-cylinder reciprocating piston engine.
In this prior art steam motor, the fuel is burned in a pore burner (CPS cell). This is a thermal reactor wherein the combustion process takes place within a porous, ceramic matrix. The distribution of the pore size can be such that a large spectrum of fuels such as natural gas, hydrogen, propane, butane and all automobile fuels can be used. Such a pore burner is described in U.S. Pat. No. 5,522,723 issued on Jun. 4, 1996 to Franz Durst et al. The disclosure of this patent is incorporated in the present specification by reference.
The steam motor described in the prior art mentioned above was, at first, conceived as a drive engine for motor cars. In the second-mentioned paper, the usefulness of the steam engine in block heating power stations or as auxiliary power units (APU) is mentioned. The particular advantages of this steam motor are low emissions without after-treatment of waste gas, high torque, flexibility with regard to fuels, variable coupling-out of thermal and mechanical energy, good efficiency, low noise and oil-free operation of the whole system The prior art steam motor suffers from the disadvantages, that it is bulky because the reciprocating piston engine is bulky itself and also because of the components required for steam generation and heat retrieval, and, therefore, can be used only where sufficient space is available. Therefore, the prior art steam motor is less suitable for the use as APU, which has to meet high demands with regard to compactness.
It is an object of the invention to provide a particularly compact steam motor without adversely affecting the efficiency as compared to the prior art steam motor.
To this end, a rotary piston engine is used as piston engine, instead of the reciprocating piston engine of the prior art steam motor. Such a rotary piston engine has high power density in relation to the space required. Furthermore, the additional systems required for the steam generation can be assembled in a much more appropriate and space-saving way around the rotary piston engine, whereby a extraordinarily compact and rugged unit is obtained. Such unit is particularly adapted for use as APU. A further advantage is that such steam engine does not generate vibrations, as there are no reciprocating masses. The rotary masses can be completely balanced. In addition, higher efficiency can be expected.
The term xe2x80x9crotary piston enginexe2x80x9d as used herein in contrast to xe2x80x9creciprocating piston enginexe2x80x9d is to include all types of engines in which the pressure of the steam or other pressurized fluid acts on surfaces of a rotor.
Further objects and modifications of the invention will be apparent to those skilled in the art when reading the following description of a preferred embodiment in conjunction with the accompanying drawings.
Embodiment if the invention are described in greater detail herein below with reference to the accompanying drawings.